The applicant is developing an automated sorting system for mined material. The applicant is also developing a system for forming microfractures in mined material. Both systems expose mined material (on a fragment-by-fragment basis or on a bulk basis) to microwave radiation to facilitate downstream processing of the fragments.
In general terms, the method of sorting mined material being developed by the applicant as part of the automated sorting system includes the following steps:
(a) exposing mined material (on a fragment-by-fragment basis or on a bulk basis) to microwave radiation and heating the mined material,
(b) detecting fragments of the mined material after the mined material has been exposed to microwave radiation,
(c) using detected data and assessing the fragments on the basis of composition (including grade of a valuable metal) or texture or another characteristic of the fragments, and
(d) physically separating fragments based on the assessment in step (c).
The purpose of exposing mined material to microwave radiation is to cause a change in the mined material that provides information on characteristics of the mined material that is helpful for sorting and ultimately downstream processing of fragments of the mined material and that can be detected by one or more than one sensor. The information may include any one or more of the characteristics of composition (including grade of a valuable metal), mineralogy, hardness, porosity, structural integrity, dielectric properties, and texture of the mined material.
The term “fragment” is understood herein to mean any suitable size of mined material having regard to materials handling and processing capabilities of the apparatus used to carry out the method and the downstream processing requirements. In the context of ore sorting, relevant factors include issues associated with detecting sufficient information to make an accurate assessment of the mined material in the fragment. It is also noted that the term “fragment” as used herein may be understood by some persons skilled in the art to be better described as “particles”. The intention is to use both terms as synonyms.
Automated ore sorting technology known to the applicant is limited to low throughput systems, typically less than 100 tonnes/hr. The general approach used in these low throughput sorting systems is to convey ore fragments through sorters on a horizontal belt. The applicant has realised that there is a number of issues to be addressed in developing higher throughput automated sorting systems.
One issue for the technology development path of the applicant relates to ensuring that all of the mined material being processed is exposed to at least a minimum power density, i.e. the amount of energy per m3 in the heated phase, to provide an accurate basis on which to assess the fragments of the mined material to allow sorting of the mined material into an “accepts” category and a “rejects” category that are above and below a threshold assessment parameter, respectively. Grade of a valuable metal is one example of a threshold parameter. An added dimension to this issue is to expose mined material to microwave radiation at high throughputs. A further dimension to this issue in a number of commercially important situations is to expose mined material having low concentrations of valuable material to microwave radiation and obtain a response to the microwave radiation that can provide an accurate basis on which to assess the fragments of the mined material.
The system for forming microfractures in fragments of mined material being developed by the applicant includes exposing fragments to electromagnetic radiation such as microwave radiation to form microfractures in the fragments. The microfractures facilitate downstream processing of the fragments to recover valuable material, such as valuable metals, from the fragments. The downstream processing options include, by way of example, heap leaching, with the microfractures allowing leach liquor to penetrate the fragments and improve recovery of valuable metals. Another downstream processing option includes comminuting the fragments and forming smaller fragments, processing the smaller fragments in a flotation circuit and forming a concentrate and smelting the concentrate to recovery valuable metals. As is the case with ore sorting technology discussed above, the technology for forming microfractures in fragments of mined material known to the applicant is limited to low throughput systems.
An issue for the technology development paths of the applicant in the fields of sorting fragments and forming micro-fractures in fragments relates to ensuring that all of the mined material being processed is exposed to at least a minimum power density of electromagnetic radiation that is required for downstream processing of the fragments.
Rectangular box-shaped, i.e. cuboid, microwave radiation heating applicators that have side walls that define a chamber that is rectangular in transverse cross-section and in longitudinal cross-section are a proven and tested design that is used extensively in domestic microwave heating applications. These applicators are hereinafter referred to as “rectangular applicators”.
The inventors have found that such rectangular applicators have features that could be advantageous when applied to applicators for use in processing mined material at high throughputs, for example by exposing mined material to microwave radiation in automated sorting systems and forming microfractures in fragments of mined material. The features include ease of design, low electric field strength leading to reliable power delivery, ease of impedance matching, and large size.
However, the inventors have also found that rectangular applicators have disadvantages including low supported power density in a heated phase, very heterogeneous power density distribution, and difficulties in vapour extraction. As a consequence, the inventors have concluded that rectangular applicators are not suitable for the automated sorting system and the microfracturing system being developed by the applicant.
The above description is not to be taken as an admission of the common general knowledge in Australia and elsewhere.